Unreliable flow can lead to poor plant performance and even equipment damage; to counter this Mass Flow should be encouraged. Mass Flow occurs when all the hopper’s contents are in motion whenever any discharge takes place. Mass Flow should be employed when any of the following conditions apply:
1.If the material’s behaviour is adversely affected by extended storage time. For example, if the material goes off, 'cakes', sinters, ferments or degrades in any way, it is necessary to ensure that there are no static regions when the bin contents are discharging. Mass flow gives ‘first in, first out’ inventory control.
2.If the material is free flowing and composed of granules or powders of differing size. Accretion of fractions or different components of blends can give rise to many issues, including segregation. Where these cause operational or quality problems, mass flow should be used to minimise the separation and generate a degree of re-mixing during discharge.
3.If the discharged material has to be in a consistent condition of density, and avoid being too loose and fluid-like, or is to be metered on a volumetric basis. Situations where this is necessary include packing into big bags, discharging to filling machines that must hold a given weight via a volumetric filler, bag fillers that require a settled density to hold the capacity or to a screw feeder that requires the product to have a consistent density.
4.If the material entering the bin is very fine, retaining air for a long time and thus maintaining a fluid-like state. It is essential to prevent a core flow channel passing through the contents when the bin is emptied by giving time for the fresh material to de-aerate to a stable flow condition.
(double click on picture to open in new window)
Mass Flow, 4 Types of Internal Core Flow and Expanded Flow
(from left to right)
5.If cohesive and non-free flowing materials are used. For materials that make a 'snowball' when compressed in the hand, the outlet size required for reliable discharge is smaller with Mass Flow. In a Mass Flow channel the bulk will continually deform and flow. Where an 'expanded flow' channel will secure the outlet benefits of Mass Flow, the non-mass flow region has to be designed to avoid the formation of 'ratholes'.
6.If there is a changeover of product on a continuous flow system, as with some extruder feeds, then Mass Flow is needed to avoid extended cross contamination of the stock.
7.If gas counter-flow systems are used, as with the stripping of volatile gasses from the interstitial voidage, or heating and cooling in continuous flow systems. Mass Flow will secure the most even flow velocity profiles and bulk porosity conditions across the moving bed of solids.
If you need help or advice in achieving reliable flow, contact Ajax.
AJAX Top Tips: Achieving Reliable Flow 1 - Mass Flow
AJAX Top Tips:
Achieving Reliable Flow 1 – Mass Flow
Unreliable flow can lead to poor plant performance and even equipment damage; to counter this Mass Flow should be encouraged. Mass Flow occurs when all the hopper’s contents are in motion whenever any discharge takes place. Mass Flow should be employed when any of the following conditions apply:
1.If the material’s behaviour is adversely affected by extended storage time. For example, if the material goes off, 'cakes', sinters, ferments or degrades in any way, it is necessary to ensure that there are no static regions when the bin contents are discharging. Mass flow gives ‘first in, first out’ inventory control.
2.If the material is free flowing and composed of granules or powders of differing size. Accretion of fractions or different components of blends can give rise to many issues, including segregation. Where these cause operational or quality problems, mass flow should be used to minimise the separation and generate a degree of re-mixing during discharge.
3.If the discharged material has to be in a consistent condition of density, and avoid being too loose and fluid-like, or is to be metered on a volumetric basis. Situations where this is necessary include packing into big bags, discharging to filling machines that must hold a given weight via a volumetric filler, bag fillers that require a settled density to hold the capacity or to a screw feeder that requires the product to have a consistent density.
4.If the material entering the bin is very fine, retaining air for a long time and thus maintaining a fluid-like state. It is essential to prevent a core flow channel passing through the contents when the bin is emptied by giving time for the fresh material to de-aerate to a stable flow condition.
(double click on picture to open in new window)
Mass Flow, 4 Types of Internal Core Flow and Expanded Flow
(from left to right)
5.If cohesive and non-free flowing materials are used. For materials that make a 'snowball' when compressed in the hand, the outlet size required for reliable discharge is smaller with Mass Flow. In a Mass Flow channel the bulk will continually deform and flow. Where an 'expanded flow' channel will secure the outlet benefits of Mass Flow, the non-mass flow region has to be designed to avoid the formation of 'ratholes'.
6.If there is a changeover of product on a continuous flow system, as with some extruder feeds, then Mass Flow is needed to avoid extended cross contamination of the stock.
7.If gas counter-flow systems are used, as with the stripping of volatile gasses from the interstitial voidage, or heating and cooling in continuous flow systems. Mass Flow will secure the most even flow velocity profiles and bulk porosity conditions across the moving bed of solids.
If you need help or advice in achieving reliable flow, contact Ajax.
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